1. Field of the Invention
The system of this invention relates to the demodulation of coherent phase-shift-keyed signals. More particularly, this system applies to the demodulation of such signals that are modulated by orthogonal or bi-orthogonal codes.
2. Description of the Prior Art
Prior art systems for the demodulation of coherent phase-shift-keyed signals typically use a local phase reference signal which is phase locked to the unmodulated phase of the received signal. As a consequence, such systems normally require a "start-up" period at the beginning of operation during which the phase of the local reference signal is adjusted so as to lock onto or become in phase with the unmodulated phase of the received signal. As a consequence, in the systems of the prior art, an unmodulated signal is normally transmitted during this "lock in" period as no data is transmitted or received during this period. Furthermore, if phase synchronization or "lock in" is lost during the period when data is being transmitted, the data received while "lock on" is being re-established is lost. In some systems of the prior art, the transmission of data must be interrupted and an unmodulated signal transmitted in order to re-establish "lock on."